Machine-readable security element for security products

ABSTRACT

The present invention relates to a machine-readable security element for security products which comprises at least one particulate substance having electroluminescent properties and a transparent, electrically conductive pigment, to a priming ink for the production of a security element of this type, and to a security product which includes the security element.

The present invention relates to a machine-readable security element forsecurity products which emits visible and machine-detectable radiationafter contactless excitation in an electric alternating field, to aprinting ink for the production of a security element of this type, andto security products which include a security element of this type.

Security products, such as banknotes, cheques, credit cards, shares,passports, identity documents, driving licences, entry tickets, valuestamps and the like, have for many years been provided with varioussecurity features which are intended to make counterfeiting of theseproducts more difficult.

Security products are preferably provided with various security elementswhich belong to different security levels. It is of major advantage hereif one and the same security element simultaneously belongs to aplurality of security levels, i.e. if a limited area of a securityproduct can be verified both optically without aids and also with aids,the perceptible optical impression generally being different. It isparticularly desirable for a security element of this type which hasdifferent security levels to be produced in a simple, preferably single,process step.

These security elements include those which comprise substances havingelectro luminescent properties. These are taken to mean substances whichemit visible radiation due to excitation in an electric alternatingfield.

In order to be able to detect a security element of this type, thesecurity product must be excited using an electric alternating field.

Security elements which comprise substances having electroluminescentproperties are known.

Thus, DE 41 26 051 describes a security document having an embeddedsecurity thread which has electroluminescent properties. This securitythread has a multi-layered structure and contains a layer comprising anelectroluminescent substance between two electrically conductive layerswhich act as electrodes.

Light emission can only be detected in the case of this particularstructure and with direct electrical contacting of the electrodes.

DE 197 35 293 discloses a value and security product having aluminescent element. The luminescent element is located in a layer ofthe security product which is arranged below a layer having anauthenticity feature. It thus serves as backlighting for the overlyingauthenticity element.

The design of the authenticity element is of secondary importance here.In addition, it does not necessarily have to be optically visiblewithout aids. A laser-capable poly-carbonate film is described asauthenticity element. The electroluminescent element is produced byprinted-on electrodes and substances having electroluminescentproperties located in a separate layer.

This structure is very complicated and likewise only allowscontact-encumbered production of the electroluminescence.

A value and security product having a similar structure is described inDE 197 08 543. The electroluminescent substances here, which are printedon, are arranged in such a way that the field lines of the electricalternating field which are generated by the planar electrodearrangement pass through them. Here too, contactless production of theelectroluminescence is not possible.

EP 1 156 934 B1 discloses a document of value which contains at leastone optically variable material and at least one machine-readablefeature material, where the feature material is in the form of a code oralphanumeric information, and the optically variable material is apigment. The machine-readable feature material here must not impair thevisible, optically variable effect of the optically variable material.The machine-readable feature material can be, inter alia, a luminescentsubstance, an electrically conductive polymer, carbon black or the like.These are generally employed alternatively.

The luminescent substances described are those which emit light outsidethe visual spectral region. Substances having electroluminescentproperties are not mentioned.

The electrically conductive polymer or the carbon black is employed forthe production of electrically conductive layers.

The machine-readable feature material can either be located in the samelayer as the optically variable material or alternatively in a separatelayer. Although two different security levels are advantageouslycombined with one another in this document of value, themachine-readable feature is a feature which can be detected under IR orUV light and cannot be machine-read using special checking equipmentwhich produces an electric alternating current field. However, thisequipment is principally employed in professional checking equipment fordocuments of value, such as, for example, automatic banknote countersand checkers.

The object of the present invention was therefore to provide amachine-readable, electroluminescent security element for securityproducts which has luminescence which can be evaluated by machine oncontactless excitation in an electric alternating field, has a simplestructure, is preferably transparent, can be applied to a securityproduct by means of a simple process and into which a further securitylevel can be integrated in a simple manner.

A further object was to provide a printing ink for the production of asecurity element of this type.

Furthermore, an additional object of the present invention was toprovide a pigment mixture which can be employed for a printing ink forthe production of a security element having the above-mentionedproperties.

Finally, a further object of the present invention was to provide asecurity product which includes a security element which has highelectroluminescence intensity on contactless excitation by an electricalternating field.

The object according to the invention is achieved by a machine-readablesecurity element for security products which comprises at least oneparticulate substance having electroluminescent properties and atransparent, electrically conductive pigment.

The object according to the invention is furthermore achieved by aprinting ink for the production of a security element which comprises atleast one particulate substance having electroluminescent properties anda transparent, electrically conductive pigment.

The object according to the invention is in addition achieved by asecurity product which comprises a single- or multilayered supportmaterial and at least one machine-readable security element having theabove-described composition arranged on or within a layer of the supportmaterial.

For the purposes of the invention, security products are taken to meandocuments of value, such as banknotes, cheques, credit cards, shares,passports, identity documents, driving licences, entry tickets, valuestamps, labels, packaging materials, seals and the like, but likewisearticles of daily use to be safeguarded, such as, for example, clothing,shoes, household articles, consumer electronic articles and the like,where the security element according to the invention is applieddirectly to the article.

The security element according to the invention comprises at least oneparticulate substance having electroluminescent properties and atransparent, electrically conductive pigment.

The substances having electroluminescent properties are generallyparticulate materials which comprise inorganic compounds from groups IIand VI of the Periodic Table, for example ZnS or CdS, which have beendoped or activated with metals, such as Cu, Mn or Ag. It is likewisepossible to employ particulate luminescent substances based onsilicates, aluminates, phosphates, tungstates, germanates, borates,etc., which have predominantly been activated using Mn, Sr or using rareearths, in particular substances based on Zn₂SiO₄:Mn, or alsoparticulate organic polymers, or mixtures of the above-mentionedcompounds.

After excitation in an electric alternating field, these substances emitvisible radiation. The emission of visible light preferably takes placealone or predominantly through excitation in an electric alternatingfield and to a lesser extent also through excitation in the ultravioletor infrared spectral region.

The particles are advantageously in the form of microencapsulatedcompounds. Highly suitable materials for the encapsulating layer are, inparticular, polymers or also various metal oxides. These protect theelectroluminescent substances against various environmental influences,for example against the wet components of the printing ink, which cancause decomposition of the electroluminescent substances on long-termexposure. In addition, the ageing resistance of the electroluminescentsubstances can be increased or their light emission modified by filterlayers.

The particle size of the particles is selected in such a way that theyare suitable for printing processing and in particular for gravureprinting. Average particle sizes which are suitable for this purpose arepreferably in the range from about 0.2 to about 100 μm, preferably from1 to 50 μm and particularly preferably from 2 to 30 μm.

In order to ensure that excitation of the luminescence does not occur inthe ultraviolet spectral region, UV filter layers may additionally beapplied to the surface of the electroluminescent particles.

It is also possible to add inorganic or organic dyes to the particulateelectroluminescent substances so that the reflection bands or absorptionbands of these substances shift. It is thus possible significantly tobroaden the range of available hues for light emission, since theoriginally usable base materials only emit a small number of hues.

The particulate electroluminescent substances are employed individuallyor in a mixture of two or more different substances. if differentsubstances are employed, it is advantageous for these to emit radiationof different colours.

The transparent, electrically conductive pigments employed are pigmentswhich have at least one transparent, electrically conductive layer.

Preference is given to the use of pigments which have at least onetransparent, electrically conductive layer on a substrate selected fromthe group consisting of TiO₂, synthetic or natural mica, otherphyllosilicates, glass, SiO₂ and/or Al₂O₃.

It is particularly preferred here for the said substrates to be in flakeform. In principle, however, the use of pigments which have at least onetransparent, electrically conductive layer on a non-flake-form substratecomprising the above-mentioned materials is also suitable. Transparentpigments which consist of an electrically conductive material arelikewise suitable. It is particularly advantageous for the electricallyconductive pigments to have smoothly rounded-off shapes without corners,sharp edges or projecting points, both in cross section and also in thelongitudinal axis. The use of the non-flake-form pigments is restrictedmerely by the applicational properties in the security element accordingto the invention.

In general, the electrically conductive layer or the electricallyconductive material comprises one or more conductive, doped metaloxides, such as, for example, tin oxide, zinc oxide, indium oxide ortitanium oxide, which have been doped with gallium, aluminium, indium,thallium, germanium, tin, phosphorus, arsenic, antimony, selenium,tellurium and/or fluorine.

The above-mentioned transparent conductive pigments may, if a substrateis present, have one or more further layers above and/or below theconductive layer. These layers can comprise metal oxides, metal oxidehydrates, metal suboxides, metal fluorides, metal nitrides, metaloxynitrides or mixtures of these materials.

The application of these additional layers allows the colour propertiesof the pigments to be matched to the users requirements, in particularif the additional layers are located below the conductive layer. Theapplication of additional layers above the conductive layer enables theconductivity to be matched specifically to the application'srequirements.

It has been observed that it is, for example, entirely advantageous fora dielectric layer to be located above the conductive layer, thisdielectric layer preventing direct contact of the conductive layers inthe case of mutual contact of conductive pigments in the securityelement according to the invention.

A particularly preferred material for a transparent, electricallyconductive pigment is a mica coated with at least one electricallyconductive metal-oxide layer. Particular preference is given here to amica pigment coated with a layer of antimony-doped tin oxide, a micapigment coated with a titanium-oxide layer, a silicon-oxide layer and anantimony-doped tin-oxide layer, or a mica pigment coated with anantimony-doped tin-oxide layer and a further metal-oxide layer, inparticular a titanium-oxide layer.

Such pigments are commercially available from Merck KGaA under the nameMinatec®.

The transparent, electrically conductive pigment in the security elementaccording to the invention must have adequately high transparency at thesame time as high electrical conductivity. For this reason, it isnecessary for the particle diameter of the pigment to be in a range from1 to 500 μm, preferably from 2 to 100 μm and particularly preferablyfrom 5 to 70 μm. A narrow particle-size distribution is preferred.

The aspect ratio, i.e. the ratio of the average diameter to the averagethickness of the pigments, in the case of flake-form conductive pigmentsis at least 2:1, but preferably at least 10:1 and particularlypreferably at least 100:1.

Electrically conductive flake-form pigments which have proven to beparticularly transparent while having high conductivity are those of thecomposition described above whose number-weighted Mean particle area F₅₀is greater than or equal to 150 μm², in particular greater than or equalto 200 μm². These have even more advantageous properties if thenumber-weighted proportion of pigments having a particle area of lessthan 80 μm² is less than or equal to 33% and preferably less than 25%,based on the transparent conductive pigments. However, still bettertransparency is obtained if the number-weighted proportion of pigmentshaving a particle area of less than 40 μm² is less than or equal to 15%and preferably less than or equal to 10%, based on the transparentconductive pigments. The reduction in the fines contents results in areduction in light scattering and thus in the haze in the securityelement according to the invention.

The particle area is taken to mean the value for the size of theprincipal surface of the flakes, namely the surface having the longestaxis.

The fines content is monitored, for example, by measurement under themicroscope and counting the measured particles. This can be carried outvisually, if desired simplified by comparisons of the samples againstcounted standards, or automatically with the aid of a video camera andsuitable automatic image-analysis software. Automatic analysis systemsof this type for particle-size analysis are known to the person skilledin the art and are commercially available. For statistically guaranteedparticle-size analysis, at least 1000 and preferably 2000 particles ormore should be measured.

The transparent, electrically conductive pigment can be employed in thesecurity element according to the invention individually or as a mixtureof two or more different pigments. The variety here can consist both inthe use of pigments comprising different materials, having differentshapes and/or having different colours. Only the optical transparency ofthe material must be ensured.

In order to achieve good machine-readability with sufficiently highelectroluminescence intensity, it is essential that the security elementof the present invention comprises both substances havingelectroluminescent properties and also transparent, electricallyconductive pigments, since the presence of the latter causes an increasein the electroluminescence intensity of the former and thus generatesmachine-readability.

If the security element according to the invention is to have a furthersecurity level in addition to the machine-readable electroluminescence,it may additionally also comprise at least one flake-form effect pigmentand/or an organic or inorganic coloured pigment.

Flake-form effect pigments are taken to mean flake-form pearlescentpigments, predominantly transparent or semitransparent interferencepigments and metal-effect pigments. Liquid-crystal pigments, so-calledLCPs, or structured polymer flakes, so-called holographic pigments, arealso counted amongst these. These flake-form pigments are built up fromone or more layers of materials, which may be different if desired.

Pearlescent pigments consist of transparent flakes-of high refractiveindex and exhibit a characteristic pearlescence on parallel alignmentdue to multiple reflection. Pearlescent pigments of this type whichadditionally also exhibit interference colours are known as interferencepigments.

Although classical pearlescent pigments, such as TiO₂ flakes, basic leadcarbonate, BiOCl pigments or nacreous pigments, are of course inprinciple also suitable, the flake-form effect pigments preferablyemployed for the purposes of the invention are interference pigments ormetal-effect pigments which have at least one coating of a metal, metaloxide, metal oxide hydrate or mixtures thereof, a metal mixed oxide,metal suboxide, metal oxynitride, metal fluoride, BiOCl or a polymer onan inorganic flake-form support. The metal-effect pigments preferablyhave at least one metal layer. The inorganic flake-form supportpreferably consists of natural or synthetic mica, kaolin or otherphyllosilicates, of glass, SiO₂, TiO₂, Al₂O₃, Fe₂O₃, polymer flakes,graphite flakes or of metal flakes, such as, for example, of aluminium,titanium, bronze, silver, copper, gold, steel or various metal alloys.

Particular preference is given to supports of mica, glass, graphite,SiO₂, TiO₂ and Al₂O₃ or mixtures thereof.

The size of these substrates is not crucial per se. The substratesgenerally have a thickness of between 0.01 and 5 μm, in particularbetween 0.05 and 4.5 μm. The extension in the length or width is usuallybetween 1 and 250 μm, preferably between 2 and 200 μm and in particularbetween 2 and 100 μm. They generally have an aspect ratio (ratio of theaverage diameter to the average particle thickness) of 2:1 to 25,000:1and in particular 3:1 to 2000:1.

A coating applied to the support preferably consists of metals, metaloxides, metal mixed oxides, metal suboxides or metal fluorides and inparticular of a colourless or coloured metal oxide selected from TiO₂,titanium suboxides, titanium oxynitrides, Fe₂O₃, Fe₃O₄, SnO₂, Sb₂O₃,SiO₂, Al₂O₃, ZrO₂, B₂O₃, Cr₂O₃, ZnO, CuO, NiO or mixtures thereof.

Coatings of metals preferably comprise aluminium, titanium, chromium,nickel, silver, zinc, molybdenum, tantalum, tungsten, palladium, copper,gold, platinum or alloys thereof.

The metal fluoride employed is preferably MgF₂.

The flake-form effect pigments employed are particularly preferablymultilayered effect pigments. These have a plurality of layers, whichpreferably consist of the above-mentioned materials and have variousrefractive indices in such a way that in each case at least two layersof different refractive index alternate on the support, on a flake-form,preferably non-metallic support, where the refractive indices in theindividual layers differ by at least 0.1 and preferably by at least 0.3.The layers located on the support can be either virtually transparent orcoloured or semitransparent.

The so-called LCPs, which consist of crosslinked, aligned, cholestericliquid crystals, or alternatively structured polymer flakes known asholographic pigments, can likewise be employed as flake-form effectpigments.

The flake-form effect pigments described above may be presentindividually or in a mixture in the security element in accordance withthe present invention.

The flake-form effect pigments employed in accordance with the inventionare preferably transparent or semitransparent, i.e. they transmit atleast 10% of the incident light. Flake-form effect pigments of this typeare preferably used since their transparency contributes to a widevariety of possible background colours in a security product which has asecurity element in accordance with the present invention and at thesame time the intensity of the light emission generated byelectroluminescence is not impaired.

In certain embodiments of the present invention, however, it isadvantageous if a flake-form effect pigment which has at least one metallayer is employed.

In a particularly preferred embodiment of the present invention, use ismade of a flake-form effect pigment which leaves behind a differentvisually perceptible colour and/or brightness impression at differentillumination and/or viewing angles. In the case of different colourimpressions, this property is known as colour flop. In particular,pigments which have a colour flop produce uncopyable colour and glossimpressions which are readily perceptible with the naked eye withoutaids in the security elements produced therewith. Such pigments are alsoknown as optically variable.

The optically variable flake-form effect pigments in accordance with theinvention preferably have at least two and at most four opticallyclearly distinguishable discrete colours at at least two differentillumination or viewing angles, but preferably have two opticallyclearly distinguishable discrete colours at two different illuminationor viewing angles or three optically clearly distinguishable discretecolours at three different illumination or viewing angles. In each case,only the discrete hues and not intermediate hues are preferably present,i.e. a clear change from one colour to another colour is evident ontilting the security element which comprises the optically variablepigments. This property on the one hand makes it easier for the viewerto recognise the security element as such and at the same time makescopying of this feature more difficult since colour-flop effects cannotbe copied and reproduced in commercially available colour photocopiers.

However, it is of course also possible to employ optically variableflake-form effect pigments which have a colour progression, i.e. manydifferent hues, such as, for example, the typical pearlescence, ontilting via different illumination and/or viewing angles. Diffuse colourchanges of this type are also readily detectable by the human eye.

In order to be able to develop their full optical effect, it isadvantageous if the flake-form effect pigments employed in accordancewith the invention are in aligned form in the security elementcomprising them, i.e. they are aligned virtually parallel to thesecurity-product surfaces provided with the security element. Analignment of this type generally already essentially takes place bymeans of the processes usually used for application of the securityelement, such as, for example, conventional printing processes.

Flake-form effect pigments that can be employed are, for example, thecommercially available interference pigments available under the namesIriodin®, Colorstream®, Xirallic®, Lustrepak®, Colorcrypt®, Colorcode®and Securalic® from Merck KGaA, Mearlin® from Mead, metal-effectpigments from Eckhard and goniochromatic (optically variable) effectpigments, such as, for example, Variochrom® from BASF, Chromafflair®from Flex Products Inc., Helicone® from Wacker or holographic pigmentsfrom Spectratec, and other commercially available pigments of the sametype. However, this list should merely be regarded as illustrative andnot restrictive.

Suitable inorganic coloured pigments are all customary transparent andopaque white, coloured and black pigments, such as, for example, BerlinBlue, bismuth vanadate, goethite, magnetite, haematite, chromium oxide,chromium hydroxide, cobalt aluminate, ultramarine, chromium/iron mixedoxides, spinels, such as Thenard's Blue, cadmium sulfides and selenides,chromate pigments or carbon black, while organic coloured pigments whichmay be mentioned are, in particular, quinacridones, benzimidazoles,copper phthalocyanine, azo pigments, perinones, anthanthrones, furtherphthalocyanines, anthraquinones, thioindigo and derivatives thereof, orCarmine Red. In general, all organic or inorganic coloured pigments, inparticular those which are customary in the printing sector, can beemployed.

For screening against ultraviolet radiation, it is also possible toemploy pigments which absorb UV light. Of these, titanium dioxide andzinc oxide may be mentioned merely by way of example.

The particle size of the inorganic and organic coloured pigments is notlimited, but must be matched to the requirements of the application ofthe security element on or in a security product, for example by meansof a printing process.

The security element according to the invention is applied over theentire surface or to part of a security product.

In the simplest variant, this is carried out with the aid of a printingink in a standard printing process.

Accordingly, the present invention also relates to a printing ink forthe production of a security element which comprises at least oneparticulate substance having electro-luminescent properties and atransparent, electrically conductive pigment.

Suitable as particulate substance having electroluminescent propertiesand as transparent, electrically conductive pigments are the materialsalready described above.

The said pigments and particles are present in the printing inkaccording to the invention in a suitable concentration such thatprinting of the ink is still possible without problems. Thus, theconcentration of the particulate substance having electroluminescentproperties in the printing ink is about 0.01 to 20% by weight,preferably 1 to 10% by weight and particularly preferably 2 to 8% byweight, based on the printing ink. By contrast, the transparent,electrically conductive pigment is generally present in the printing inkin a concentration of about 0.01 to about 20% by weight, preferably 1 to10% by weight and particularly preferably 2 to 8% by weight, based onthe printing ink.

In the case where the security element according to the invention isalso intended to comprise flake-form effect pigments and/or organic orinorganic coloured pigments, these are present in the printing ink inaccordance with the present invention in a concentration of about 0.01to about 40% by weight, preferably 2 to 20% by weight and particularlypreferably 5 to 15% by weight, based on the printing ink.

The said pigments and particles can be added to the printing inkindividually or in a mixture. This can take place in the form of thepulverulent pigments and particles. However, the above-mentionedpigments and particles are preferably introduced into the printing inkaccording to the invention individually or in a mixture of at least twodifferent types thereof in the form of flowable pigment compositions ordry preparations. Besides the pigment constituents, these also compriseat least one suitable binder. Thus, for example, a pigment compositionor a dry preparation can be prepared from a mixture of a particulatesubstance having electroluminescent properties and a transparent,electrically conductive pigment, with which one or more effect and/orcoloured pigments are optionally also admixed. individual compositionsor other combinations are likewise possible. Flowable pigmentcompositions are taken to mean, in particular, pastes or slurries,which, besides the said pigments, may also comprise binders, solventsand optionally one or more additives. The said dry preparationsgenerally comprise the same additives, but with a very substantiallyreduced solvent content. However, preparations which comprise 0 to 8% byweight, preferably 2 to 8% by weight and in particular 3 to 6% byweight, of water and/or a solvent or solvent mixture are also regardedas dry preparations. These dry preparations are preferably in the formof pearlets, briquettes, pellets, granules, chips, sausages or insimilar forms and generally have particle sizes of about 0.2-80 mm.Flowable pigment compositions and dry preparations of this type simplifythe transport, storage and uniform introduction of the pigments into theprinting ink, prevent separation of pigments and further constituentsand promote good redispersion behaviour of the printing inks.

Besides the pigment constituents, the printing ink according to theinvention comprises one or more suitable binders and optionally furtheradditives, such as solvents, adhesion promoters, dispersion aids, dryingaccelerators, photoinitiators and the like, which are customary inprinting inks. It goes without saying that these binders and additivesare matched to the printing process to be used and that the printing inkhas an appropriate viscosity. It should be ensured here that onlybinders and additives which essentially do not increase the electricalconductivity in the security element produced using the printing ink areselected, so that the formation of continuous conductivity in thesecurity element is prevented. The concentration of the transparent,electrically conductive pigment can also be selected within theabove-mentioned limits in such a way that continuous conductivity doesnot arise in the security element.

Suitable printing processes are in principle all printing processeswhich are known and customary in the production of security products,such as, for example, offset printing, letterset printing, offsetcoating, flexographic printing, screen printing, thermal sublimationprinting, gravure printing, in particular halftone photogravure printingand recess printing, the overprint varnish process, and all contactlessprinting processes. However, the printing ink according to the inventionis particularly preferably used in the screen printing process.

However, it is also possible to employ other coating methods, such as,for example, knife coating, brushing, stamping, pouring methods,lacquering methods, flow methods, roller or grid application methods orapplication by means of air brush.

The security element in accordance with the present invention can alsobe in the form of a polymeric layer which is present on or in a securityproduct over the entire surface or in a part-area.

A further preferred embodiment of the invention is therefore a polymericlayer which represents the security element according to the inventionand is located on or in a security product.

This polymeric layer comprises at least one particulate substance havingelectro-luminescent properties and a transparent, electricallyconductive pigment. in a preferred embodiment, the polymeric layeradditionally comprises at least one flakeform effect pigment and/or atleast one organic or inorganic coloured pigment.

The polymeric layer can be, for example, a film laminated or stuck to asecurity product over the entire surface or, for example, a filmcoextruded with other polymer films (with or without security elements).Also suitable are rigid sheets of polymeric materials which compriseboth transparent, electrically conductive pigments and also particulateelectroluminescent substances and are bonded in a conventional manner,for example by adhesive bonding, to other layer materials, optionallycarrying information. These films or sheets can be located either on thesurface of a security product or alternatively in an interlayer which issurrounded on both sides by other polymer layers. However, they can alsoform per se the base, i.e. the support material of a security product.

The thickness of the polymer layers, the polymeric material, theflexibility and the type of bonding of these layers to other layers ofthe security element are not restrictive here so long as theelectroluminescent feature is machine-readable and can clearly berecognised and evaluated due to colour and/or gloss effects produced byflake-form effect pigments or inorganic and/or organic coloured pigmentsoptionally furthermore added.

The polymeric layer may likewise be applied to part of a document ofvalue or introduced into the latter. In this case, as in the case ofprinting, any conceivable form is suitable so long as theelectroluminescence and any additional colour and gloss effects arestill clearly evident or machine-readable. All forms already mentionedfor printing are suitable. Preference is given here to the applicationor introduction of a polymeric layer in the form of a strip to or into adocument of value. If the polymeric layer is applied to an article ofdaily need to be safeguarded, it is for practical and aesthetic reasonspreferably likewise present on part of the surface thereof.

The type of application or introduction to or into part of the securityproduct should not be regarded as restrictive. For example, adhesivebonding, lamination or other common types of bonding to other materialswhich are customary for polymeric layer materials may be mentioned here.

The other layer materials preferably consist of papers of various typesor polymeric materials, but may also be textile materials or metals,etc.

If the security element according to the invention consists of apolymeric layer, the security element in the form of the polymeric layerhas two surfaces essentially parallel to one another and comprises inthe polymeric layer at least one particulate substance havingelectroluminescent properties, a transparent, electrically conductivepigment and at least one polymer.

The concentration of the particulate substance having electroluminescentproperties in the polymeric plastic is about 0.05 to 15% by weight,preferably 0.2 to 10% by weight and particularly preferably 1 to 8% byweight, based on the plastic. By contrast, the transparent, electricallyconductive pigment is generally present in a concentration of about 0.01to about 30% by weight, preferably 02 to 15% by weight and particularlypreferably 1 to 8% by weight, based on the plastic.

In the case where the security element according to the invention isalso intended to comprise flake-form effect pigments and/or organic orinorganic coloured pigments, these are present in the polymeric layer ina concentration of about 0.01 to about 40% by weight, preferably 0.1 to20% by weight and particularly preferably 1 to 10% by weight, based onthe plastic.

The pigments and particles are preferably introduced into the polymericbase composition in the form of masterbatches. Besides the pigmentconstituents, these also comprise suitable amounts of binders, solventsand optionally further customary auxiliaries and additives.

Polymers which can be employed here are all thermoplastics which exhibitan inert behaviour to the electroluminescent substances and the.transparent, electrically conductive, flake-form effect pigments. Inparticular, the polymers must not be electrically conductive or increasethe electrical conductivity of the polymeric layer. In particular, itmust be ensured that the polymeric layer as such is not continuouslyelectrically conductive although it comprises electrically conductivepigments.

The polymeric layer is preferably transparent. Preference is thereforegiven to the use of transparent polymers. This applies, for example, topolystyrene, polyvinyl chloride and copolymers and graft polymersthereof, polyvinylidene chloride and fluoride, polyamides, polyolefins,polyacrylates and polyvinyl esters, thermoplastic polyurethanes,cellulose esters and the like. They can be employed individually or insuitable mixtures.

In addition, the polymeric layer may additionally comprise customaryauxiliaries and additives, such as fillers, UV stabilisers, inhibitors,flameproofing agents, lubricants, plasticisers, solvents, dispersantsand additional dyes or organic and/or inorganic coloured pigments.

The polymeric layers are preferably produced by various suitablemethods, such as film casting, spinning, extrusion methods, calendaringor pressing methods, but in particular by extrusion methods or via afilm blowing method. To this end, the various starting materials aremixed with one another and converted into polymer layers in the form offilms of various thickness or thin sheets in suitable, generally knownequipment. The flake-form pigments (effect pigments and optionally alsothe electrically conductive pigments) present in the polymer compositionare aligned here at the surfaces of the moulds and are therefore alignedessential parallel to the surfaces of the polymeric layer in theresultant polymeric layers. Stretching and tension operations duringfilm blowing or as working steps after extrusion additionally augmentthis alignment of the pigments.

This alignment is fixed during subsequent cooling.

Separation or settling behaviour of the pigment mixture employed is notobserved in the polymeric layers.

However, it must be ensured that excessive shear forces do not act onthe pigment constituents in order to prevent destruction thereof.

Instead of into a polymeric material, the electroluminescent particulatesubstances and the transparent, electrically conductive pigments canalso be introduced into papermaking stocks or textile raw materialmixtures.

A security element of this type is produced by adding, in addition tothe said constituents, all base materials and auxiliaries which arecustomary, in particular, in papermaking. Changes in the usual processprocedure do not arise due to the particulate substances and pigments.Instead, their concentration is selected so that all standard methods,for example in papermaking, can be used. These are known to the personskilled in the art and therefore need not be explained in greater detailhere. However, it must be ensured, as already described above, that thepigments are not damaged or destroyed in the paper and textileproduction process and that continuous electrical conductivity does notarise in the resultant paper or textile.

A security element of this type can be employed as support material orsubstrate for a security product. However, it can also be attached topigmented or unpigmented substrate materials of a different or the sametype.

The present invention additionally relates to a security product whichcomprises a single- or multilayered support material and at least onemachine-readable security element arranged on or within a layer of thesupport material, where the security element comprises at least oneparticulate substance having electroluminescent properties and atransparent, electrically conductive pigment.

Optionally, but preferably, the machine-readable security elementcomprises at least one flake-form effect pigment and/or at least oneorganic or inorganic coloured pigment.

Suitable as support material for the security product according to theinvention are all customary types of paper, but in particular securitypapers having unit weights of up to 200 g/m², preferably those made fromcotton fibres, textile materials, polymeric materials, in particularpolymeric layered materials, and films of all types, as well as coatedor uncoated metal plates, metal foils and the like.

Preference is given to the use of security papers or polymer films.

The security product according to the invention is based on a single- ormultilayered support material of the above-mentioned type, where theindividual layers may consist of identical or different materials.

The security element is arranged in or on one of these layers.

If the security element according to the invention is arranged on alayer of the support material, it is then either applied over the entiresurface or to part thereof.

If it is in the form of a single security element in a security product,it is preferably applied thereto over the entire surface. These arepreferably security products having a relatively low security standard,such as, for example, packaging materials, labels, seals, entry ticketsand the like. However, application over the entire surface should alsobe considered if the security element according to the invention ispresent as the only security element on one side of the securityproduct.

In the case of security products having a high security standard, suchas, for example, banknotes, however, a plurality of different securityelements are generally present alongside one another on each side of thesecurity product. In this case, partial coating with the securityelement according to the invention comes into consideration. Thesecurity element here is applied to the security product in various,unrestricted forms, for example as strips, dots, lines, alphanumericsymbols, pictorial representations, etc. This shaping is restrictedmerely by the application method and the machine readability of theelectroluminescence or the optical perceptibility of the effect producedby the effect and/or coloured pigments. A sufficiently large area of thesecurity product should therefore be coated with the security elementaccording to the invention in order that all security levels of thesecurity element can be clearly recognised by the viewer or clearlyevaluated by machine.

If the security product is an article of daily use, such as, forexample, clothing, shoes, household articles and the like, partialcoating, which is not limited in shape and size and can advantageouslybe included in the optical design of the articles of daily use, islikewise obvious for practical reasons.

If the security element according to the invention is produced in aprinting process, it naturally comprises the above-mentioned pigmentconstituents in a higher concentration than indicated for the printingink since the solvent content is minimised after drying of the printingink.

An enhancement of the desired effects, such as optical variability oroptically visible colouring and electroluminescence properties, can beachieved if the pigment concentration in the security product accordingto the invention is increased by applying the printing ink a number oftimes one on top of the other. In this case, it is possible for thedifferent print layers to comprise pigments from in each case all oronly some of the above-mentioned three groups.

Thus, multiple application of printing inks which comprise atransparent, electrically conductive, flake-form pigment enhances theelectroluminescence properties of the security element.

The coloured and/or preferably optically variable properties of thesecurity element can be influenced by applying a plurality of layerscomprising coloured pigments, effect pigments or preferably opticallyvariable pigments one on top of the other. in this case, it is onlynecessary for at least one layer to comprise both a particulatesubstance having electroluminescent properties and also a transparent,electrically conductive pigment.

Thus, for example, it is advantageous for a layer of this type which,besides the particulate substance having electroluminescent propertiesand the transparent, electrically conductive pigment, also comprises atransparent effect pigment to be applied to a layer which comprises asemitransparent or opaque effect pigment. It is also possible for alayer comprising a transparent effect pigment to be applied to a layerwhich, besides the particulate substance having electroluminescentproperties and the transparent, electrically conductive pigment,comprises a transparent or alternatively an opaque effect pigment. Inboth cases, interesting additional colour effects or enhancements of theoriginal colour and/or gloss effect can be achieved.

The same potential variations are of course also possible if thesecurity element according to the invention is in the form of apolymeric layer which can either be bonded to other polymeric layers oralternatively overprinted and/or underprinted.

If a plurality of pigment-containing layers are applied one on top ofthe other, where at least one layer comprises the security elementaccording to the invention, the underlying and/or overlying layer canhave the same or a different shape to the security element according tothe invention.

This gives rise to large potential variations, in particular withrespect to the optically perceptible shape and colour design. Forexample, an opaque, coloured and optionally optically variablebackground applied over the entire surface is possible, which thesecurity element according to the invention in a certain shapeemphasises. It is likewise possible for at least two layers lying one ontop of the other to have the same shape and be arranged precisely oneabove the other, so that an enhancement of the optical effect is onlyvisible at this point.

In the security element in accordance with the present invention, thesaid pigment constituents are in a random distribution.

In descriptive form, the arrangement of the pigments can be described asa roof tile-like structure of the flake-form, transparent, electricallyconductive pigments preferably employed with particles havingelectroluminescent properties arranged in a scattered manner in between.If flake-form effect pigments are additionally employed, most thereof,likewise coloured pigments and binders and polymeric base compositions,have dielectric properties.

For the machine readability of the electroluminescence, it is necessaryfor the luminous intensity of the particles to be sufficiently high tobe registered and unambiguously assigned by the reader.

It is clearly evident that, due to the roof tile-like arrangement of thevarious flake-form pigments, it is not ensured that allelectroluminescent particles are on the surface of the security element.Instead, many of them are hidden by the flake-form pigments. However, anincrease in the concentration of the electroluminescent particles wouldbe accompanied by processing disadvantages.

The transparency of the electrically conductive pigments also enablesunderlying electroluminescent particles to be seen if they have asufficiently high luminescence intensity. It has also proven to beparticularly advantageous for both transparent or at leastsemitransparent flake-form effect pigments and also transparent,electrically conductive flake-form pigments to be employed. These do nothinder the view of the electroluminescent pigments lying under them.

In order to be able to detect the electroluminescence in the securityelement according to the invention by machine, the security productwhich has the security element is introduced into an electricalternating field.

In principle, the arrangements and checking equipment described in DE197 58 587 C2 are suitable for measurement of the electroluminescence inthe security element according to the invention.

The field lines of the electric alternating field penetrate through thesecurity element according to the invention and are deflected by thetransparent, flake-form, electrically conductive pigments, so thatpartial amplification of the electric field occurs. The electromagneticwaves amplified in this way result in increased excitation of theparticles having electroluminescent properties and provoke increasedemission of luminescence radiation there, which can be unambiguouslyregistered and assigned by the measuring instrument.

In principle, an amplification of this type of the luminescenceradiation would also be achievable with non-transparent, electricallyconductive pigments, for example with metal pigments or pigments whichcomprise metal layers. However, their opacity to light inevitablyresults in high pigment concentrations with respect to theelectroluminescent particles having to be employed, since particleslying under the non-transparent pigments are completely covered. Suchhigh pigment concentrations are disadvantageous.

In addition, combinations with coloured underprints, as described above,are not possible on use of opaque, electrically conductive pigments.

It has furthermore been found that security elements produced withopaque, electrically conductive pigments, in particular those havingmetal layers, lose their electrical conductivity on subsequentmechanical stressing of the security product, whether by printing platesor in particular by conventional subsequent embossing printingprocesses, although their optical properties which may also be presentare retained. The electroluminescence in the security element isconsequently then no longer sufficient to be unambiguouslymachine-readable.

It was therefore extremely surprising that a combination of electricallyconductive, non-transparent pigments, in particular those having metallayers, which in this case are employed as effect pigments, withtransparent, electrically conductive pigments and electroluminescentparticles in accordance with the present invention results in securityelements which have both the optical properties of metallic effectpigments and also a sufficiently high machine-readableelectroluminescence, even when they are subjected to subsequentmechanical stresses, for example during an embossing printing process.

This is therefore a further preferred embodiment of the presentinvention.

The security element in accordance with the present invention has anumber of advantages compared with the known solutions of the prior art.Since contactless machine detection of electroluminescent radiation isoften unsuccessful on sole use of suitable amounts of electroluminescentmaterials in security elements, and security elements having integratedelectrodes have a complicated structure, it is a major advantage of thepresent invention to have solved the problem of contactless measurementof electroluminescence by addition of a single further material. At thesame time, it has been observed that the machine checking of thesecurity element according to the invention takes less time than thechecking of other security elements, meaning that it can readily beintegrated into the existing checking process, for example of banknotes.

In order to achieve the object according to the invention, it issufficient merely to add two different particulate materials in suitableamounts, for example to a printing ink, so that the security element inaccordance with the present invention also has a simple structure, whichcan be achieved in the simplest case via printing onto a customarysubstrate. Polymeric layers which represent the security elementaccording to the invention have a similarly simple structure.

Both prints and also polymeric layers can, due to their transparency, becombined extremely well with visible, in particular coloured, overlyingor underlying layers. At the same time or alternatively, however, thesecurity element according to the invention may itself also compriseeffect and/or coloured pigments, which may themselves represent asecurity feature which can be detected optically without aids.

Since many electroluminescent substances also have photoluminescentproperties, this can, if necessary, result in integration of a furthersecurity level, which can be verified, for example, using a UV lamp.

The security element in accordance with the present invention thereforerepresents an excellent way of being able to combine a plurality ofsecurity features belonging to different security levels with oneanother at a single point of a security product in addition tocontactless machine readability of electroluminescent properties. Thecounterfeiting security of security products is thus greatly increased.

1-22. (canceled)
 23. A printing ink for the production of a securityelement comprising at least one particulate substance havingelectroluminescent properties and a transparent, electrically conductivepigment, said printing ink comprising at least one particulate substancehaving electroluminescent properties and a transparent, electricallyconductive pigment.
 24. The printing ink according to claim 23, furthercomprising at least one flake-form effect pigment and/or at least oneorganic or inorganic colored pigment.
 25. The printing ink according toclaim 23, wherein said pigments and particles are employed in the formof a pigment mixture which comprises at least two different types ofthese pigments and/or particles.
 26. The printing ink according to claim25, wherein said pigment mixture further comprises at least one binder.27. The printing ink according to claim 26, wherein said pigment mixtureis in the form of pearlets, briquettes, pellets, granules, chips,sausages, a paste or a slurry.
 28. The printing ink according to claim23, further comprising at least one binder.
 29. The printing accordingto claim 28, further comprising one or more solvents, adhesionpromoters, dispersion aids, drying accelerators or photoinitiators. 30.A pigment mixture for a printing ink for the production of a securitycomprising at least one particulate substance having electroluminescentproperties and a transparent, electrically conductive pigment, saidpigment mixture comprising at least one binder and at least twodifferent types of pigment selected from particulate substances havingelectroluminescent properties, transparent, electrically conductivepigments, flake-form effect pigments and inorganic or organic coloredpigments.
 31. The pigment mixture according to claim 30, which is in theform of a flowable pigment composition or dry preparation. 32.(canceled)
 33. (canceled)
 34. (canceled)
 35. (canceled)
 36. The printingink according to claim 24, wherein said pigments and particles areemployed in the form of a pigment mixture which comprises at least twodifferent types of these pigments and/or particles.
 37. The printing inkaccording to claim 36, wherein said pigment mixture further comprises atleast one binder.
 38. The printing ink according to claim 37, whereinsaid pigment mixture is in the form of pearlets, briquettes, pellets,granules, chips, sausages, a paste or a slurry.
 39. The printing inkaccording to claim 23, wherein said transparent, electrically conductivepigment and said at least one particulate substance havingelectroluminescent properties are in a random distribution.
 40. Theprinting ink according to claim 23, wherein the concentration oftransparent, electrically conductive pigment is such that the formationof continuous conductivity in the resultant security element isprevented.
 41. The printing ink according to claim 39, wherein theconcentration of transparent, electrically conductive pigment is suchthat the formation of continuous conductivity in the resultant securityelement is prevented.